Practice neco computer_studies 2025 Past Questions

Question 1 View Details

A relation R(A,B,C,D,E) has the set of functional dependencies: $ A \rightarrow B $, $ B \rightarrow C $, $ C \rightarrow D $, $ D \rightarrow E $, and $ A \rightarrow E $. Decompose R into BCNF using the standard decomposition algorithm. State the resulting relations, indicate whether the decomposition is lossless‑join, and comment on dependency preservation.

A. Relations: R1(A,B), R2(B,C), R3(A,E), R4(D,E). Lossless‑join: Yes. Dependency preservation: A→B, B→C, C→D are preserved; D→E is not preserved.

Correct B. Relations: R1(A,B), R2(B,C), R3(A,D), R4(D,E). Lossless‑join: Yes. Dependency preservation: A→B, B→C and D→E are preserved; C→D is not preserved.

C. Relations: R1(A,B), R2(B,C), R3(C,D), R4(D,E). Lossless‑join: Yes. Dependency preservation: A→B, B→C, C→D and D→E are preserved.

D. Relations: R1(A,B), R2(B,C), R3(A,D), R4(D,E). Lossless‑join: No. Dependency preservation: Only A→B and B→C are preserved.

Correct Answer: B

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Question 2 View Details

The following Python program is intended to compute the sum of all integers $ \le n $ that are prime and whose digit‑sum is also prime. However, it contains a logical error. Identify and correct the error, then determine the value returned by the corrected program when $ n = 30 $. Also state the asymptotic time‑complexity of the program in Big‑O notation.\n\n```python\ndef is_prime(k):\n if k < 2:\n return False\n for j in range(2, int(k**0.5) + 1):\n if k % j == 0:\n return False\n return True\n\ndef special_sum(n):\n total = 0\n for i in range(2, n): # <-- error here\n if is_prime(i):\n s = sum(int(d) for d in str(i))\n if is_prime(s):\n total += i\n return total\n```

A. 78; O(n\\log n)

B. 84; O(n\\sqrt{n})

C. 80; O(n\\log n)

Correct D. 80; O(n\sqrt{n})

Correct Answer: D

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Question 3 View Details

A processor has a base CPI of 1.0. The instruction mix is 30% loads/stores, 20% branches, and the remaining 50% are ALU operations. The data‑cache has a hit rate of 95% with a miss penalty of 100 cycles; a cache hit costs 1 cycle. The branch predictor is 80% accurate and a misprediction costs 5 cycles. Assuming stalls are the only source of CPI increase, calculate the average CPI of the processor.

A. 2.9

B. 2.5

C. 3.0

Correct D. 2.7

Correct Answer: D

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Question 4 View Details

An organisation evaluates the risk of a ransomware attack. The likelihood of the threat occurring is 0.3, the vulnerability rating is 0.4, and the impact rating is 0.8 (all on a scale from 0 to 1). Compute the overall risk score as the product of these three factors. Then, identify which of the three security principles - confidentiality, integrity, or availability - is most directly compromised by a successful ransomware attack.

A. Risk = 0.32; most compromised principle = integrity

B. Risk = 0.12; most compromised principle = integrity

C. Risk = 0.24; most compromised principle = availability

Correct D. Risk = 0.096; most compromised principle = confidentiality

Correct Answer: D

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Question 5 View Details

A loan of $ \text{₦}500{,}000 $ is to be repaid over 5 years with monthly payments. The monthly payment $ P $ is given by the amortisation formula $ P = L \frac{r(1+r)^{n}}{(1+r)^{n}-1} $, where $ L $ is the loan amount, $ r $ is the monthly interest rate and $ n $ is the total number of payments. If the observed monthly payment is $ \text{₦}9{,}500 $, determine the annual nominal interest rate (to two decimal places). Show the steps you would use in a spreadsheet to obtain the rate (e.g., using Goal Seek or the RATE function) and give the resulting rate.

A. 6.12%

Correct B. 5.23%

C. 5.78%

D. 4.87%

Correct Answer: B

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Question 6 View Details

The following pseudocode is executed: ``` count = 0 for i = 1 to n for j = 1 to i for k = 1 to (n - i + 1) count = count + 1 ``` Express the total number of times the statement `count = count + 1` is executed as a function of $n$. Then find the smallest integer $n$ for which this total exceeds 10,000.

A. 40

Correct B. 39

C. 41

D. 38

Correct Answer: B

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Question 7 View Details

An 11‑bit sequence is transmitted as follows: the first 8 bits are data, bit 9 is an even‑parity bit for the data, and bits 10‑11 form a 2‑bit checksum equal to the sum (mod 4) of the decimal values of the first two 4‑bit nibbles. The received sequence is $10110011001$. Determine whether a transmission error occurred and, if so, identify the erroneous bit position (counting from the left, 1‑indexed).

A. 5

B. 9

Correct C. 4

D. 3

Correct Answer: C

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Question 8 View Details

Consider a relation $R(A,B,C,D,E)$ with the functional dependencies:\n\n1. $A \rightarrow B$\n2. $B \rightarrow C$\n3. $AD \rightarrow E$\n4. $CD \rightarrow A$\n\nDetermine all candidate keys of $R$ and state the highest normal form (1NF, 2NF, 3NF, or BCNF) that $R$ satisfies.

A. Candidate keys: AD, CD; Highest normal form: 2NF

B. Candidate keys: AD, CD, BD; Highest normal form: BCNF

C. Candidate keys: AB, AC, BD; Highest normal form: 3NF

Correct D. Candidate keys: AD, CD, BD; Highest normal form: 3NF

Correct Answer: D

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Question 9 View Details

In a spreadsheet, column A holds product codes (text), column B holds quantity sold (integer), and column C holds unit price (currency). Column D should display the revenue for each row using the following rules: - If quantity $\ge 100$, apply a 10 % discount to the unit price. - Else if the product code starts with "X" **and** quantity $< 50$, apply a 5 % surcharge to the unit price. - Otherwise use the unit price unchanged. Write the Excel formula for cell D2 (assuming the data start in row 2). Then, using the data below, compute the total revenue (sum of D2:D4). | Row | A (code) | B (qty) | C (price) | |-----|----------|----------|-----------| | 2 | X12 | 30 | 20 | | 3 | A5 | 120 | 15 | | 4 | X99 | 80 | 10 |

A. 2960

B. 3020

C. 3090

Correct D. 3050

Correct Answer: D

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Question 10 View Details

A message "DATA" is encrypted with a Caesar cipher using an unknown shift $k$ (0 ≤ k ≤ 25). The observed ciphertext is "GDWD". Determine the shift $k$. Afterwards, briefly state (in no more than 30 words) whether employing this cipher for transmitting confidential data is ethically acceptable, given its security level.

A. 3; Caesar cipher provides strong security, making its use ethical.

B. 5; Caesar cipher is insecure for confidential data, so its use is unethical.

C. 7; Caesar cipher is insecure for confidential data, but its use is acceptable.

Correct D. 3; Caesar cipher is insecure for confidential data, so its use is unethical.

Correct Answer: D

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Question 11 View Details

A motherboard has four DDR4 DIMM slots. Each slot can hold a memory module of at most $8$ GB. What is the maximum total RAM capacity that can be installed on the board?

A. 40 GB

B. 16 GB

C. 24 GB

Correct D. 32 GB

Correct Answer: D

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Question 12 View Details

A company needs to connect 10 computers. In a star topology each computer is linked to a central switch. Five computers are $3$ m from the switch and the other five are $7$ m from the switch. In a bus topology the computers are placed linearly with $2$ m spacing between adjacent computers, and the total cable length includes the segment from the first to the last computer plus $1$ m extra for each terminator (two terminators). The cost per metre of twisted‑pair cable used for the star is ₦$150$ and the cost per metre of coaxial cable used for the bus is ₦$120$. Which topology results in the lower total cable cost? State the name of the cheaper topology.

A. Mesh topology

Correct B. Bus topology

C. Star topology

D. Ring topology

Correct Answer: B

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Question 13 View Details

An organization requires passwords to be exactly six characters long. Each character can be an uppercase letter ($26$ choices), a digit ($10$ choices), or one of the five special symbols (!, @, #, $, %). A valid password must contain at least one digit and at least one special symbol. How many distinct passwords satisfy the policy? Give your answer as an integer.

A. 2573321905

Correct B. 1994734000

C. 1994765000

D. 1685818224

Correct Answer: B

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Question 14 View Details

The company database has two tables. The Employees table records each employee's department and salary, while the Departments table records each department's budget. The number of employees, the average salary per employee, and the budget for each department are given below:\n\n\begin{array}{c|c|c|c}\text{DeptID} & \text{Employees} & \text{Avg Salary (₦)} & \text{Budget (₦)}\\\hline\n1 & 15 & 200{,}000 & 4{,}000{,}000\\\n2 & 20 & 150{,}000 & 3{,}500{,}000\\\n3 & 10 & 180{,}000 & 2{,}500{,}000\\\n4 & 25 & 210{,}000 & 6{,}000{,}000\\\n5 & 12 & 190{,}000 & 3{,}000{,}000\\\n6 & 8 & 170{,}000 & 2{,}000{,}000\\\n7 & 20 & 160{,}000 & 4{,}500{,}000\\\n8 & 10 & 175{,}000 & 2{,}800{,}000\end{array}\n\nFor each department compute the total salary expense (number of employees $\times$ average salary) and determine whether it exceeds $80\%$ of the department's budget. List the DeptIDs, in ascending order, of the departments where the total salary expense exceeds $80\%$ of the budget.

A. 1, 3

B. 2, 5

Correct C. 2, 4

D. 4, 7

Correct Answer: C

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Question 15 View Details

A USB\,3.0 port can supply up to $5$ V at $900$ mA. What is the maximum power, in watts, that can be drawn from a single USB\,3.0 port? Give your answer to two decimal places.

Correct A. 4.50 W

B. 4.95 W

C. 5.00 W

D. 4.00 W

Correct Answer: A

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Question 16 View Details

Consider the following Python program:\n\n```python\ndef f(x):\n s = 0\n while x > 0:\n d = x % 10\n s += d*d\n x //= 10\n return s\n\nn = int(input())\ncount = 0\nfor num in range(1, n+1):\n if num % 2 == 0 and f(num) % 3 == 0:\n count += 1\nprint(count)\n```\n\nIf the user enters $ n = 30 $, what integer is printed?

A. 3

B. 0

Correct C. 2

D. 1

Correct Answer: C

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Question 17 View Details

A school is deciding between two office‑automation software packages.\n\nPackage A costs $ \text{₦}120,000 $ initially. Its annual maintenance fee is 12 % of the purchase price and a one‑time upgrade cost of $ \text{₦}30,000 $ is required after the third year.\n\nPackage B costs $ \text{₦}150,000 $ initially. Its annual maintenance fee is 8 % of the purchase price and a one‑time upgrade cost of $ \text{₦}20,000 $ is required after the second year.\n\nAssuming the school will use the software for exactly five years and will pay the maintenance fee each year, which package has the lower total cost over the five‑year period?

A. Both packages have equal total cost

B. Package B

Correct C. Package A

D. Package A with a lower maintenance fee

Correct Answer: C

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Question 18 View Details

A school wants to divide the network $ 192.168.20.0/24 $ into four equal sub‑networks, each of which must support at least 30 usable host addresses. Determine the subnet mask that should be used and give the network address together with the range of usable host addresses for each of the four sub‑nets.

A. Subnet mask 255.255.255.224. The four sub‑nets are: 192.168.20.0/27 (hosts .1‑.30), 192.168.20.32/27 (hosts .33‑.62), 192.168.20.64/27 (hosts .65‑.94), 192.168.20.128/27 (hosts .129‑.158)

B. Subnet mask 255.255.255.224. The four sub‑nets are: 192.168.20.0/27 (hosts .1‑.30), 192.168.20.32/27 (hosts .33‑.62), 192.168.20.96/27 (hosts .97‑.126), 192.168.20.128/27 (hosts .129‑.158)

C. Subnet mask 255.255.255.192. The four sub‑nets are: 192.168.20.0/26 (hosts .1‑.62), 192.168.20.64/26 (hosts .65‑.126), 192.168.20.128/26 (hosts .129‑.190), 192.168.20.192/26 (hosts .193‑.254)

Correct D. Subnet mask 255.255.255.224. The four sub‑nets are: 192.168.20.0/27 (hosts .1‑.30), 192.168.20.32/27 (hosts .33‑.62), 192.168.20.64/27 (hosts .65‑.94), 192.168.20.96/27 (hosts .97‑.126).

Correct Answer: D

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Question 19 View Details

Consider the following pseudocode:\n\n``\ncount = 0\nfor i = 1 to n do\n j = i\n while j <= n do\n count = count + 1\n j = j + i\n end while\nend for\n``\n\nExpress the total number of times the statement `count = count + 1` is executed as a function of $ n $, and state the time‑complexity of the algorithm using Big‑O notation.

A. T(n)=\\sum_{i=1}^{n} \\left\\lceil \\frac{n}{i} \\right\\rceil, which is \\Theta(n), therefore the time‑complexity is O(n).

B. T(n)=\\sum_{i=1}^{n} i, which is \\Theta(n^{2}), therefore the time‑complexity is O(n^{2}).

Correct C. T(n)=\sum_{i=1}^{n} \left\lfloor \frac{n}{i} \right\rfloor, which is \Theta(n \log n); therefore the time‑complexity is O(n log n).

D. T(n)=\\sum_{i=1}^{n} \\frac{n}{i}, which is \\Theta(n \\log n), therefore the time‑complexity is O(n \\log^{2} n).

Correct Answer: C

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Question 20 View Details

In which year was the first commercially successful microprocessor, the Intel 4004, released?

A. 1974

B. 1970

C. 1972

Correct D. 1971

Correct Answer: D

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Question 21 View Details

Consider the following pseudo‑code where $n = 60$: for i = 1 to n for j = 1 to i if $i \bmod 3 = 0$ then execute S How many times is statement S executed?

A. 315

B. 600

Correct C. 630

D. 660

Correct Answer: C

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Question 22 View Details

Given the HTML element: ```html <div id="header" class="nav main"></div> ``` and the following CSS rules: ```css .nav { color: blue; } #header { color: red; } div.main { color: green; } div#header.nav { color: purple; } * { color: black; } ``` What is the final computed colour of the <div> element?

Correct A. purple

B. blue

C. green

D. red

Correct Answer: A

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Question 23 View Details

Let $R(A,B,C)$ and $S(B,D)$ be two relations. Consider the relational‑algebra query: \[ \pi_{A,D}\bigl(\sigma_{C>10}(R) \;\bowtie_{R.B = S.B}\; \sigma_{D<5}(S)\bigr) \] Rewrite the query so that selections and projections are applied as early as possible, thereby minimising the size of intermediate results. Provide the equivalent expression.

A. π_{A,D}( (π_{A,B}(σ_{C>10}(R))) ⨝_{R.B = S.B} (π_{B,D}(σ_{D<5}(S))) )

B. π_{A,D}( (π_{A,C}(σ_{C>10}(R))) ⨝_{B = B} (π_{B,D}(σ_{D<5}(S))) )

C. π_{A,D}( (π_{A,B}(σ_{C>10}(R))) ⨝_{B = B} (σ_{D<5}(S)) )

Correct D. π_{A,D}( (π_{A,B}(σ_{C>10}(R))) ⨝_{B = B} (π_{B,D}(σ_{D<5}(S))) )

Correct Answer: D

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Question 24 View Details

The following JavaScript code attaches click handlers to three list items: ```html <ul id="menu"> <li>Item 1</li> <li>Item 2</li> <li>Item 3</li> </ul> ``` ```js var items = document.querySelectorAll('#menu li'); for (var i = 1; i <= items.length; i++) { items[i-1].addEventListener('click', function() { alert('You clicked item ' + i); }); } ``` When the user clicks on **Item 3**, what message is displayed?

A. You clicked item 2

Correct B. You clicked item 4

C. You clicked item 3

D. You clicked item 5

Correct Answer: B

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Question 25 View Details

The CSS below defines a flex container with media queries: ```css .container { display: flex; flex-direction: row; } @media (max-width: 800px) { .container { flex-direction: column; } } @media (min-width: 1000px) { .container { flex-direction: row-reverse; } } ``` HTML: ```html <div class="container"> <div class="a">A</div> <div class="b">B</div> <div class="c">C</div> </div> ``` What is the visual order of the letters when the viewport width is **750 px** and when it is **1100 px**?

Correct A. At 750 px: A, B, C (top to bottom); At 1100 px: C, B, A (left to right)

B. At 750 px: A, C, B (top to bottom); At 1100 px: C, A, B (left to right)

C. At 750 px: B, A, C (top to bottom); At 1100 px: B, C, A (left to right)

D. At 750 px: C, B, A (top to bottom); At 1100 px: A, B, C (left to right)

Correct Answer: A

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